Oracle Offline Persistence Toolkit - Reacting to Replay Conflict

This is next post related to Oracle Offline Persistence Toolkit. Check my previous writing on same subject - Implementing Handle Patch Method in JET Offline Toolkit. Read more about toolkit on GitHub repo.

When application goes online, we call synchronisation method. If at least one of the requests fails, then synchronisation is stopped and error callback is invoked, where we can handle failure. In error callback, we check if failure is related to the conflict - then we open dialog, where user will decide what to do (to force client changes or take server changes). Reading latest change indicator value from response in error callback (to apply it, if user decides to force client changes in the next request):

Dialog is simple - it displays dynamic text for conflicted value and provides user with a choice of actions:

Let's see how it works.

User A editing value Lex and saving it to backend:

User B is offline, editing same value B and saving it in local storage:

We can check it in the log - changes value was stored in local storage:

When going online, pending requests logged offline, will be re-executed. Obviously above request will fail, because same value was changed by another user. Conflict will be reported:

PATCH operation fails with conflict code 409:

User will be asked - how to proceed. To apply changes and override changes in the backend, or on opposite take changes from the backend and bring them to the client:

I will explain how to implement these actions in my next post. In the meantime you can study complete application available on GitHub repo.

Query Logic Implementation in VBCS for ADF BC REST

Oracle Visual Builder Cloud Service allows to define external REST service connections. In this post I will explain how to implement query logic against such service. Connection is defined for ADF BC REST service.

Wizard provides option to add query parameters, both static and dynamic. I have set one static parameter onlyData=true, to return data only from the service. Also I have created multiple dynamic parameters, the one used in this use case - q parameter. This parameter accepts query expression to filter data. Later in VBCS action chain, I will assign value to this parameter and service will be re-executed to bring filtered data:

Search form elements will be assigned with page scope variables, to hold user query input. On search button click, VBCS action chain will be invoked to read these values and update query parameter. Page scope variables:

Variables firstNameQueryVar and lastNameQueryVar are assigned to search form fields, here is example:

Search button invokes action chain:

Action chain does two things - calls JS function to construct query parameter and then assigns returned value to rest service query parameter to execute search:

JS function is mapped to accept input parameters from search form input fields:

JS function code - parameters are joined into ADF BC REST query string:

JS function result is mapped with page scope variable - result is assigned to this variable:

REST service query parameter q variable is assigned with this value. Once value changes, query is automatically re-executed:

In my next post I will explain how to implement filtering and pagination with transformation function, on top of service connection:

VBCS sample application code is available on GitHub (if you download ZIP from GitHub, make sure to extract it and create new archive including extracted content directly, without top folder).

Implementing Handle Patch Method in JET Offline Toolkit

When executing PATCH requests offline, JET Offline Persistence Toolkit will record that request and synch it to the backend, once online. But it will not update data stored in cache, this is by design. Since cached data will not be updated, search queries against offline cache would not bring results based on latest changes. To solve this we need to implement cache update ourself by providing handle patch method.

Handle patch is configured through requestHandlerOverride property while registering persistence manager:

Sample implementation for handle patch. This method is invoked, when PATCH is executed while offline only. We must read information from request and pass it to cache store. Search for entry in cache based on key, updating record and updating info back to the store:

Let's do offline test - switch browser tab to be offline (you can do it Chrome browser developer tools). Do search and check log from JET Offline Persistence Toolkit - it executes search automatically against cache store:

Update same record, while offline - PATCH request will be recorded for later synchronisation. Our handle patch method will be invoked to write changes to cache store:

You will notice in the log, actions executed from handle patch method. It finds record by key in cache and updates it:

Search by updated value - updated value is found and returned from cache store:

Code is available in GitHub repository.

ADF BC REST Query and SQL Nesting Control Solution

I will talk about expert mode View Object (with hand written SQL), this View Object is created based on SQL join. So, thats my use case for today example. I will describe issue related to generated SQL statement and give a hint how to solve it. This is in particular useful, if you want to expose complex VO (SQL with joins and calculating totals) over ADF BC REST service and then run queries against this REST resource.

Code is available on my GitHub repository.

Here is SQL join and expert mode VO (the one where you can modify SQL by hand):

This VO is exposed through ADF BC REST, I will not go through those details, you can find more info about it online. Once application is running, REST resource is accessible through GET. ADF BC REST syntax allows to pass query string along with REST request, here I'm filtering based on StreetAddress='ABC':

On backend this works OK by default and generates nested query (this is expected behaviour for expert mode VOs, all additional criteria clauses will be added through SQL wrapping). While such query executes just fine, this is not what we want in some use cases. If we calculate totals or average aggregated values in SQL, we don't want it to be wrapped:

To prevent SQL wrapping we can call ADF BC API method in VO constructor:

While probably this works with regular ADF BC, it doesn't work with criteria coming from ADF BC REST. SQL query is generated with two WHERE clauses, after query nesting was disabled:

Possible solution proposed by me - override executeQueryForCollection method, do some parsing and change second WHERE to be AND, apply changed query string and then execute super:

This trick helps and query is generated as we would expect, criteria added from ADF BC REST query call is appended at the end of WHERE clause:

Flow Navigation Menu Control in Oracle VBCS

Oracle VBCS allows us to build multiple flows within the application. This is great - this helps to split application logic into different smaller modules. Although VBCS doesn't offer (in the current version) declarative support to build menu structure to navigate between the flows. Luckily this requirement can be achieved in few simple steps, please read John Ceccarelli post - Adding a Navigation Bar to a VBCS Application. I thought to go through instructions listed by John and test it out, today post is based on this. In my next posts I will take a look how to replace navigation bar menu structure with something more advanced, for example - menu slider on the left.

I think VBCS have great potential as JavaScript declarative development IDE. I see many concepts are similar to other Oracle declarative development tools, e.g. Forms, Oracle ADF. VBCS runs Oracle JET, all you build in VBCS is Oracle JET. Oracle takes care upgrading Oracle JET version in VBCS, I have applied recent patch (by click of the button) and latest JET version is available within our VBCS environment:

Coming back to flows in VBCS. We can create as many flows we want. Each flow could be based on one or multiple fragments (HTML/JS modules). Here I have created three flows, each with single fragment:

We can select flow and this will bring us flow diagram, where we could have navigation implementation between flow elements/fragments:

Fragment - this is where UI part is done:

So thats about flows and fragments. For someone with ADF background, this sounds very similar to task flows and fragments. Next we should see how to implement flow navigation, to be able to select flow from the top menu. VBCS application comes with so called shell page. This page is top UI wrapper, which contains application name, logged user info, etc. Here we can implement top level menu, which would navigate through application flows:

There must be default flow, which is displayed once application is loaded. Default flow is set in settings of the shell page. Go to settings and choose default flow, dashboard-flow in my case:

Next we need to add JET component - navigation list to the shell page, to render menu UI. You can do it by drag and drop, but easier is to switch shell page to source view and add navigation list HTML portion manually (you can copy paste it from source code uploaded to GitHub, see link at the end of this post) - highlighted HTML will render menu bar to navigate between flows:

Initially you will notice error related to JET navigation list not recognised, we need to import it. Another error - selection listener is not found, we will implement it.

To import JET navigation list component, go to source implementation of the shell page and add oj-navigation-list in component imports section - this will solve issue with unknown navigation list entry:

To execute action in VBCS, we must create Action Chain. Crete Action Chain within shell page - navigateToPage:

We need input parameter - flow name, which want navigate to. Create variable in Action Chain - currentFlow:

Add action of type Navigate to Action Chain, this will trigger navigation logic:

Go to Action Chain source and add "page": "{{$variables.currentFlow}}" under actions. This will force navigation to the flow, which will be passed through parameter:

Finally we create navigation list selection event (within shell page), this event will trigger action chain created above and pass current flow ID. We must create custom event and its name should match even name defined in JET navigation list in HTML (see above):

Choose to create custom event (it didn't work for me in Chrome, only in Safari browser. VBCS bug?) and provide same name as in navigation list component listener:

Choose our navigation Action Chain to be triggered from this event:

Just a reminder, event is called from navigation list selection:

Event is passing flow ID from currently selected tab item:

On runtime, dashboard flow is loaded by default:

We can switch to Jobs, etc.:

Download exported (runnable only in VBCS) VBCS app from GitHub repo.